fix(pg-cursor): settle read() when rowCount exceeds remaining rows

[dyk1454683243-sudo]

Fixes #2949

Problem

cursor.read(rowCount) never called its callback when rowCount was larger than the remaining (or total) rows. A table with 100 rows and read(1000) hung instead of returning the leftover rows.

PostgreSQL reports portal exhaustion with CommandComplete, not PortalSuspended. pg-cursor only delivered the current batch from PortalSuspended or ReadyForQuery. After CommandComplete the cursor closed the portal and sent Sync, then waited for ReadyForQuery. If that message was never dispatched to the cursor, read() never settled.

A late RowDescription could also reset a busy cursor to idle and start a queued execute, overwriting the in-flight callback. Queued read() calls were never drained when the portal was exhausted.

Fix

In packages/pg-cursor:

• Deliver the in-flight read() as soon as CommandComplete arrives (shorter or empty batch).
• Resolve any queued reads with [] once the portal is exhausted.
• Do not start a queued execute from RowDescription / noData while a read is already in flight.
• Clear the current callback synchronously so a later ReadyForQuery cannot deliver the same batch twice.

Tests

packages/pg-cursor/test/read-exhaustion.js:

• Unit: oversized read() settles on CommandComplete without ReadyForQuery.
• Unit: leftover rows after a partial page, then an oversized read().
• Unit: queued reads settle with [] after exhaustion.
• Unit: late RowDescription does not overwrite an in-flight oversized read.
• Integration: 100 rows, read(1000) returns 100, then [].
• Integration: read(40) then read(1000) returns the remaining 60.

Claim check

Searched open and recently updated PRs on brianc/node-postgres and dyk1454683243-sudo/node-postgres for #2949, cursor.read hang, and rowCount. Issue #2949 is still open with no linked closer. No existing PR owns this fix.

Verification

• packages/pg-cursor: 49 passing (including the new cases)
• packages/pg-query-stream: 40 passing
• eslint on the changed files: clean